Biological carbon sequestration is enhanced under activity centers of the endangered Yucatán black howler monkey (Alouatta pigra)

Background/Question/Methods

Tropical forests are the largest terrestrial reservoir of biological carbon (C). When undisturbed, these forests serve as important sinks for C from the atmosphere. However, when forests undergo deforestation, they switch from being C sinks to sources. Recent research has focused on how habitat destruction impact C dynamics of forests. Far fewer studies consider how loss of biodiversity and ecological interactions influence these processes. To fill this gap, we combined tree surveys and an allometric approach to understand how aboveground tree biomass (AGB) and biological C were influenced by occupancy of the endangered Yucatán black howler monkey in subtropical forests in Belize. We hypothesized that monkeys enhance AGB and C sequestration by promoting successful establishment of trees with high wood density via selection, pre-processing, and dispersal of seeds during frugivory. We conducted tree surveys within 20-diameter plots under six separate howler troops, paired with six random plots 50-m distant from these activity centers. Trees were identified and DBH was measured. We used a database to assign wood density and calculate AGB. Differences in richness, diversity, DBH, wood density, AGB, and biological C were evaluated using paired t-tests. Additionally, we tested for compositional differences in the tree communities using PERMANOVA.

Results/Conclusions

Within our plots (n=12), we found 432 trees representing 36 species from 34 genera in 21 families. Species richness (t = 1.15, df = 5, p = 0.30) and Shannon H (t = -0.366, df = 5, p = 0.7293) did not differ with monkey occupancy, the average being 6.75 and 0.90 respectively. Monkey occupancy did not influence average DBH (t = 1.8308, df = 5, p = 0.1266) or wood density (t = 1.3439, df = 5, p = 0.2367), the averages being 45.19 cm and 0.545 g cm-3 respectively. We observed a 180% increase in AGB (and therefore, biological C) in plots under monkey troops compared to the paired unoccupied plots (553.87 ±110.78 versus 197.67 ±61.83 Mg ha-1; t = 2.6438, df = 5, p = 0.04577). Plant identity did not vary with monkey occupancy (pseudo-F1,10 = 0.69, p = 0.86). We conclude that howler monkeys have the potential to positively influence carbon sequestration where they occur. Conservation of keystone frugivores may be an important climate change mitigation strategy due to their potential ability to enhance carbon sequestration.